<template>
    <div>
        <input ref="excel-upload-input" class="excel-upload-input" type="file" multiple="multiple" accept=".xlsx, .xls" @change="handleClick"/>
        <div class="drop" @drop="handleDrop" @dragover="handleDragover" @dragenter="handleDragover">
            将 excel 文件拖放到此处或
            <el-button :loading="loading" style="margin-left:16px;" size="mini" type="primary" @click="handleUpload">
                浏览
            </el-button>
        </div>
    </div>
</template>

<script>
import XLSX from "xlsx";

export default {
    props: {
        beforeUpload: Function, // eslint-disable-line
        onSuccess: Function // eslint-disable-line
    },
    data() {
        return {
            loading: false,
            excelData: {
                header: null,
                results: null
            },
            sheets: [],
            file: null
        };
    },
    methods: {
        generateData({header, results}) {
            this.excelData.header = header;
            this.excelData.results = results;
            this.onSuccess && this.onSuccess(this.excelData);
        },
        generateAllSheetData(workbook) {
            this.sheets = [];
            const SheetNames = [workbook.SheetNames[0]];
            // const SheetNames = workbook.SheetNames;
            const Sheets = workbook.Sheets;

            for (var i = 0; i < SheetNames.length; i++) {
                const firstSheetName = SheetNames[i];
                const worksheet = Sheets[firstSheetName];

                const header = this.getHeaderRow(worksheet);
                const results = XLSX.utils.sheet_to_json(worksheet);

                this.sheets.push({
                    header,
                    results
                });
            }

            this.onSuccess && this.onSuccess(this.sheets, this.file);
        },
        sliceInPiece(file, piece = 1024 * 1024 * 5) {
            this.file = file;
            let totalSize = file.size; // 文件总大小
            let start = 0; // 每次上传的开始字节
            let end = start + piece; // 每次上传的结尾字节
            let chunks = []
            while (start < totalSize) {
                // 依据长度截取每次须要上传的数据
                // File对象继承自Blob对象，因而蕴含slice办法
                let blob = file.slice(start, end);
                chunks.push(blob)

                start = end;
                end = start + piece;
            }
            return chunks
        },

        handleDrop(e) {
            e.stopPropagation();
            e.preventDefault();
            if (this.loading) return;
            const files = e.dataTransfer.files;
            if (files.length !== 1) {
                this.$message.error("Only support uploading one file!");
                return;
            }
            const rawFile = files[0]; // only use files[0]

            if (!this.isExcel(rawFile)) {
                this.$message.error("Only supports upload .xlsx, .xls, .csv suffix files");
                return false;
            }
            let chunks = this.sliceInPiece(rawFile)
            console.log("chunks", chunks)

            chunks.forEach(chunk => {
                console.log("chunk", chunk)
            })

            this.upload(rawFile);
            e.stopPropagation();
            e.preventDefault();
        },
        handleDragover(e) {
            e.stopPropagation();
            e.preventDefault();
            e.dataTransfer.dropEffect = "copy";
        },
        handleUpload() {
            this.$refs["excel-upload-input"].click();
        },
        handleClick(e) {
            const files = e.target.files;
            const rawFile = files[0]; // only use files[0]
            if (!rawFile) return;
            this.upload(rawFile);
        },
        upload(rawFile) {
            this.$refs["excel-upload-input"].value = null; // fix can't select the same excel

            if (!this.beforeUpload) {
                this.readerData(rawFile);
                return;
            }
            const before = this.beforeUpload(rawFile);
            if (before) {
                this.readerData(rawFile);
            }
        },
        readerData(rawFile) {
            this.loading = true;
            return new Promise((resolve, reject) => {
                const reader = new FileReader();
                reader.onload = e => {
                    const data = e.target.result;
                    const workbook = XLSX.read(data, {type: "array"});
                    this.generateAllSheetData(workbook);
                    this.loading = false;
                    resolve();
                };
                reader.readAsArrayBuffer(rawFile);
            });
        },
        getHeaderRow(sheet) {
            const headers = [];
            const range = XLSX.utils.decode_range(sheet["!ref"]);
            let C;
            const R = range.s.r;
            /* start in the first row */
            for (C = range.s.c; C <= range.e.c; ++C) {
                /* walk every column in the range */
                const cell = sheet[XLSX.utils.encode_cell({c: C, r: R})];
                /* find the cell in the first row */
                let hdr = "UNKNOWN " + C; // <-- replace with your desired default
                if (cell && cell.t) hdr = XLSX.utils.format_cell(cell);
                headers.push(hdr);
            }
            return headers;
        },
        isExcel(file) {
            return /\.(xlsx|xls|csv)$/.test(file.name);
        }
    }
};
</script>

<style scoped>
.excel-upload-input {
    display: none;
    z-index: -9999;
}

.drop {
    border: 2px dashed #bbb;
    width: 600px;
    height: 160px;
    line-height: 160px;
    margin: 0 auto;
    font-size: 24px;
    border-radius: 5px;
    text-align: center;
    color: #bbb;
    position: relative;
}
</style>
